Patent GB-538744-A (GB)
Title: Photographic view finder
IPC: G02B23/14
Filed: 1940-06-21
Abstract: 538,744. Photographic view-finders. BROOKES, N. E. (Technicolor Motion Picture Corporation). June 21, 1940, No. 10699. [Classes 97 (i) and 98 (i)] The lens of a view-finder having focusing and parallax compensating movements is simultaneously movable on tracks in directions parallel and perpendicular to the lens axis, and the ratio of these two movements can be varied to conform to the optical properties of the exchangeable finder lens in use. As shown, in a form applied to a kinematograph camera, the finder comprises an objective OF, a reflecting prism P, a framing element or matte M, magnifying viewing lenses VL1 and VL2, and a reflector R2, together with a screen S which may as shown be formed on the surface of the lens VL1, all these elements being carried by a structure secured to the side of the camera. Attached to this structure by hinges 71, and shown in Fig. 3 in its open position, is a structure carrying reflectors R3 and R4, a viewing lens (not shown) between them, and a hinged viewing-hood H. When in use, this structure is turned forwardly through a right angle from the position shown, so that the reflectors R2, R3 face one another, and is held by a latch 73, 74. The hood H is then turned down so that it faces rearwardly and the image in the reflector R4 may be viewed through it. The objective OF is interchangeably carried in a mount tube 35, being positioned by a groove and key 36 and a catch 37. The focal length of the finder objective employed is chosen in accordance with that of the camera objective, two finder objectives being generally sufficient, one for use with camera objectives of long focus and one with those of shorter focus. The lens mount tube 35 is carried on a cross slide 33 on a carriage 31 movable in a slide 17 on a bracket 16. Focusing is performed by means of cams 44, 45, one for each objective to be employed, which are carried by a shaft 41 rotatably mounted in the carriage 31, and which are selectively made to engage an abutment (not shown) on the bracket 16 by axial adjustment of the shaft 41, this adjustment being maintained by a spring catch 56 which selectively engages in grooves 53, 54, 55 in the end of the shaft. In one position a collar 46 engages the fixed abutment, in which case no focusing movement occurs. A spring 62 acting on the carriage 31 maintains the cam in contact with the abutment. Simultaneously with the focusing movement the mount 35 is given a cross movement on the carriage 31 for the correction of parallax, by means of a worm 43 splined on the shaft 41 and engaging a rack on the mount. A drum 51 carries a focusing scale for each of the cams, the axial movement of the shaft 41 bringing the correct scale into register with an index on a sleeve 59. The mount 35 is connected to the casing of the prism P by a shield plate 27 which is laterally movable in grooves and has a flange 28 slidably engaging in the mount. The lenses VL1 and VL2, as well as the interchangeable frame or matte M, are mounted in a removable drawer 21. A single lens hood 81 covers both the camera and finder objectives, louvres 82 being provided in it which screen the camera objective from side light while only slightly obstructing the field of view of the finder. In a modification applied to a camera encased in a sound-proof enclosure the structure including the reflectors R3, R4, the viewing lens, and the hood H is secured to the outer face of a door on the enclosure, and is not attached to the portion secured to the camera. In this form the viewing lens, instead of being situated between the mirrors R3, R4 is placed in an aperture in the door of the enclosure, opposite to the mirror R3.